Backup pad assembly



Aug. 6, 1968 N. MATOUKA 3,395,417

BACKUP PAD ASSEMBLY Filed April 5, 1966 INVENTOR.

United States Patent 3,395,417 BACKUP PAD ASSEMBLY Nicholas Matouka,Royal Oak, Mich, assignor to Formax Manufacturing Corporation, Detroit,Mich., a corporation of Michigan Filed Apr. 5, 1966, Ser. No. 540,372 2Claims. (Cl. -230) ABSTRACT OF THE DISCLOSURE A backup .pad constructionwith a soft flexible pad member secured to a flexible backup plate andwith a rigid insert member connected to the backup plate. The inner faceof the backup plate has spaced annularly extending grooves providingzones of flexibility.

The present invention relates to the construction of backup padassemblies. Backup pad assemblies are used to finish workpieces and aremade flexible to accommodate the different contours of the workpieces.Backup pad assemblies have been made of a backup plate of a relativelyinflexible material and a pad member which is made of a soft rubber ofplastic with the two bonded together by conventional means. With thistype of construction, substantially all of the flexibility is providedby the pad and hence a relatively thick pad member must be provided.Normally, the juncture between the pad member and backup plate is in asingle plane and hence the bond between the two is on this plane. It isimportant that this bond be secured in order to in sure that the padmember will not be torn loose from the backup plate. In presentinvention a backup plate having undulations is provided which lend bothflexibility to the backup plate and also provide for better bondingbetween the pad member and the backup plate; also, in the presentinvention because a backup plate is provided which is flexible, the padmember need not be as thick and hence a lighter backup pad assembly canbe provided. Therefore, it is an object to provide an improved backuppad assembly.

It is another object of the present invention to provide a backup padassembly in which an improved bond is provided between the pad and thebackup plate.

It is still another object of the present invention to provide a backuppad assembly in which the backup plate is flexible and enhances thetotal flexibility of the backup pad assembly.

Other objects, features, and advantages of the present invention willbecome apparent from the subsequent description and the appended claims,taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a front elevational view of a backup pad assembly embodyingfeatures of the present invention; and

FIGURE 2 is a sectional view to increased scale of the backup padassembly of FIGURE 1, taken substantially along the line 22.

Looking now to the drawings, a backup pad assembly generally indicatedby the numeral 10 and includes a pad member 12 which can be made of asoft flexible material such as a soft urethane foam and which isprovided with a tough face member 14 at its forward surface which isflat. The face member 14 is preferably made of canvas or some otherporous material whereby the urethane of the pad member 12 will flowpartially through the pores therein in molding and, hence, a secure bondis provided between the face member 14 and the forward surface of thepad member 12. The pad member 12 is secured at its opposite rearwardsurface to a backup plate 16 which can be made of a flexible materialsuch as a flexible solid urethane. While the back- "ice up plate 16 ismade of a flexible material it should be understood that it issubstantially stiffer than the pad member 12. The backup plate 16 inturn is molded to a relatively stiff mounting insert 18 which is made ofa strong and generally stiff material such as a polycarbonate. Theinsert 18 is less flexible than either the pad member 12 or the backupplate 16.

The insert 18 has a tubular portion 20 provided with a plurality ofthreads 22 whereby the backup pad assembly 10 can be mounted on one endof a threaded shaft for rotation thereby. Attached to the tubularportion 20 of the insert 18 is an annular web portion 24 which isgenerally of an irregular contour radially, The backup plate 16 has ahub portion 30 molded generally about the web portion 24 and the forwardend of the tubular portion 20.

The insert 18 being made of polycarbonate is generally stiff; however,polycarbonate is a material which is easily moldable into a selectedshape and has good strength characteristics whereby the tubular portion20 and threads 22 are strong. However, because of its lack offlexibility, the polycarbonate does not lend itself to substantialflexing and can fail under repetitive, high loads. The backup plate 16being made of a flexible solid urethane is more flexible and also hasgood fatigue characteristics and thus provides a good combination withthe polycarbonate insert 18. The backup plate 16 has an annular contourand is provided with a radially outer tapering ring portion 26 which isconnected to generally flat backed portion 28. The hub portion 30 of thebackup plate 16 generally provides the connection between the portion 28and the insert 18. The forward surface of the backup plate 16 isprovided with an annular groove 32 which is just adjacent to andsurrounds the hub portion 30. The groove 32 is contoured to projectaxially inwardly and provides at its root a reduced section portion 34.A second generally similarly constructed groove 36 is located adjacentto and surrounds the groove 32 and likewise projects axially inwardly todefine a minimum or reduced section portion 38.

The annular ring portion 26 is blended into the groove 36 and defines afrusto conical section which tapers radially outwardly to a minimumsection at its extremity.

By the provision of the grooves or undulations 32 and 36, points ofreduced sections 34 and 38 are provided which provide areas of increasedflexibility. With this construction, the flexibility of the pad assembly10 is enhanced by the backup plate 16 because of the inherentflexibility both of the flexible urethane and also because of theprovision of the areas of flexibility as at the reduced sections 34, 38.It should be noted that most of the work is done at the outer peripheraledges of the pad member 12 and hence most of the force will be appliedthereto. The pad member 12 is of a larger diameter than the backup plate16 and from a point extending radially outwardly from the groove 36 thepad member 12 gradually decreases in section. By locating a point offlexure or groove 36 near the outer end of the backup plate 16 thechange in flexibility is gradual in a radial inward direct-ion providingfor a well balanced construction. By the provision of the grooves 32 and36 the flexing of the backup and assembly 10 is caused to occur at apoint removed from the hub portion 30 and, hence, removed from thestilfer insert 18. Thus substantially little flexing is imposed upon thestiff insert member 18; since the backup plate 16 is flexible, thebackup pad assembly 10 can readily conform to the contour of the part tobe worked upon and because of the added flexibility provided by backupplate 16 the pad member 12 can be maintained at a minimum. The result isa generally lighter pad assembly 10. Note that the undulations orflexing grooves 32 and 36 provides -for a greater resultant area ofcontact between the backup plate 16 and the pad member 12; as a result,a better bond can be provided therebetween. Note also that the padmember 12 is molded to the tough front face 14 and the backup plate 16with an impervious skin formed on the exposed areas; the result is thatWater, etc. will not get into the interior of the pad member 12 and,hence, the backup pad assembly will maintain good operatingcharacteristics under working conditions.

While it Will be apparent that the preferred embodiment of the inventiondisclosed is Well calculated to fulfill the objects above stated, itwill be appreciated that the invention is susceptible to modification,variation and change without departing from the proper scope or fairmeaning of the subjoined claims.

What is claimed is:

1. A backup pad assembly comprising a pad member made of a generallyflexible material and means for supporting said pad member comprising abackup plate secured to the backside of said pad member and hub meansfor engaging said backup pad assembly for rotation, said backup platehaving flexing means comprising one area of reduced section betwen saidhub means and the radially outer periphery of said backup plate wherebysaid backup plate is flexible about said one area, said reduced sectiondefined by a first generally annularly extending groove, said hub meanscomprising an insert member of a rigid construction secured to saidbackup plate with said insert member including gripping means adapted tobe gripped for rotation, said pad member being constructed of a soft,resilient material substantially more flexible than that of said backupplate, said backup plate being constructed of a hard, resilient materialwhich is substantially more flexible than said insert member, said padmember having a generally uniform cross section from said hub meansradially outwardly through said flexing means except for said reducedsection, said flexing means comprising a second area of reduced sectionfor providing flexing of said backup pad assembly at points removed fromsaid hub means with said second area being defined by a second generallyannularly extending groove, one of said first and second grooves beinglocated near the radially outer end of said backup plate, said padmember having a portion extending radially outwardly beyond said backupplate withsaid portion tapering gradually radially outwardly of said oneof said grooves to minimum thickness.

2. The assembly of claim 1 with said pad member composed of a flexiblepolyurethane foam, with said backup plate composed of flexible solidurethane and with said insert composed of a still, rigid plastic such aspolycarbonate and with said gripping means comprising a threaded portionon said insert.

References Cited UNITED STATES PATENTS 2,217,791 10/1940 Burleigh 51-3792,229,745 1/ 1941 Kneisley 51-379 XR 2,800,751 7/1957 Bruckcr 51-3772,800,752 7/1957 Short 51-376 2,950,584- 8/1960 Welch 51-378 2,958,16611/1960 Poland 51-358 3,082,582 3/1963 Jeske 51-358 3,315,420 4/ 1967Moberg 51-378 FOREIGN PATENTS 321,223 6/ 1957 Switzerland.

DANIEL B-LUM, Primary Examiner.

